The present invention refers to check valves for medical infusion lines and the like.
Such check (or non return) valves normally incorporate a first and a second tubular element that respectively define an upstream and a downstream passageway, mutually coaxial to each other and with an elastically deformable diaphragm placed transversally between them. This diaphragm cooperates with the annular seat of the said first tubular element to form a fluid seal that maintains the check valve in the normally closed position, and in which a predetermined fluid pressure in the said upstream passageway causes a deflection of the diaphragm and consequent opening of the check valve.
Such check valves must meet a series of critical requirements: in the first place, they must normally be closed and must only open, continuously or intermittently, when the pressure in the upstream passageway is higher than a predetermined threshold, normally of small entity e.g. 0.01-0.02 bar. The check valve must also be capable of preventing any reflux from the downstream passageway to the upstream passageway with utmost security, i.e. it must be capable of rapidly closing itself in cases where a minimal overpressure enters the downstream passageway.
Another requirement of the check valves used in the medical applications in question consists in simple and low-cost realisation.
As an example, a solution that partially responds to these requirements is described and illustrated in U.S. Pat. No. 5,617,897. Here, the diaphragm has an annular peripheral section held axially between the first and second tubular elements, a central section acting like a valve obturator, and openings between the peripheral section and the central section. In this solution, it can be noted that the valve""s annular seat has an annular projection with a tapered border against which the central section of the diaphragm rests when the check valve is the closed position. A predetermined overpressure in the upstream passageway causes the diaphragm to flex due to its elastic stretching and the resulting passage of fluid from the upstream passageway to the downstream passageway via the diaphragm opening.
This solution has various drawbacks. First of all, the realisation of the projection with a tapered border in the first tubular element, for supporting the central section of the diaphragm, entails certain constructional complications. In addition, the difference in elasticity between the tapered border and the central section of the diaphragm can produce permanent local deformations on the diaphragm that reduce the reliability of check valve""s hermetic closure, with the risk of undesired reflux of fluid from the downstream passageway to the upstream passageway. Also, because the separation of the central section of the diaphragm from the valve seat of the first tubular element when the check valve is opened, is effected by elastically stretching the diaphragm, the peripheral section of which is blocked between the first and second tubular elements, the calibration of the check valve is dependent upon the elasticity characteristics of the diaphragm. As a consequence, should the elasticity of the diaphragm undergo variations during manufacture (material characteristics, moulding parameters, etc.), calibration can be subject to significant and therefore critical variations.
Other known solutions are described and illustrated in European patent application EP-A-0247824, patent U.S. Pat. No. 5.727.594 and European patent application EP-A-0934757. In all of these instances, the diaphragm has an annular peripheral section placed axially between the first and second tubular elements, a disc-shaped central section acting like a valve obturator with the said valve seat, and openings between the peripheral section and the central disc.
These known solutions have a series of common elements: first of all, the annular peripheral section of the diaphragm is thicker and seated in a complementary annular seat formed between the first and second tubular elements. Moreover, this thicker annular peripheral section is axially blocked within the seat, acting like a seal.
In the second place, when the valve is in the closed position, the membrane exhibits a more or less deformed shape in the axial direction, in the sense that the central disc section and the peripheral section are not mutually coplanar.
In addition to a more or less significant amount of axial space occupied the valve, these realisations also have constructional problems deriving from difficulties in assembling the diaphragm between the first and second tubular elements.
The object of the present invention is that of resolving these inconveniencies, this objective being principally achieved via the characteristics defined in claim 1, i.e. the fact that the said disc is moulded with a thin circumferential sealing lip, projecting axially from the side of the disc facing the said valve seat.
This solution allows the inconveniencies of the previous techniques to be eliminated and avoids the need to create an axial annular projection in the first tubular element to delineate the valve seat (as in the case of the already cited document U.S. Pat. No. 5,617,897), which simplifies the overall construction of the check valve.
The disc is conveniently moulded with an identical, axially projecting, circumferential sealing lip on the opposite face to render the diaphragm completely symmetrical, which obviously simplifies assembly operations for the check valve.
According to another aspect of the invention, the disc is connected to the peripheral section via a crown with arched arms, the aforesaid openings being between the arched arms. In this way, movement of the central disc, which forms the valve obturator, between the open and close positions relative to the valve seat is realised via the geometric lengthening of the said arched arms to a substantially straight condition and, respectively, by the said arms returning to the initial arched configuration. Due to their arched shape, the lengthening of the arms does not cause any significant elastic deformation to the diaphragm, and so the movement of the diaphragm""s central disc away from the valve seat, that is the opening of the check valve, has a substantially linear characteristic. This linearity, repeatable over time, renders calibration of the check valve in conformity with the invention extremely straightforward by simply regulating the assembly preload on the diaphragm between the first and second tubular elements.
In addition, the fact that motion of the diaphragm""s central disc when opening occurs due to the straightening of the said arched arms, or rather following their geometrical lengthening without substantial elastic stretching, renders the opening of the check valve in conformity with the invention softer and more gradual with respect to conventional check valves for a given preload.
According to a further characteristic of the invention, the said arched arms conveniently have a concave longitudinal edge and convex longitudinal edge with different curvature radii, with the former larger than the second. This characteristic allows each arm to be endowed with rapid return characteristics in the starting curve condition, and hence rapid return of the diaphragm""s central disc to the closed valve position. It is possible to change the valve""s calibration by conveniently adjusting the radius values for the concave and convex edges at the time of manufacture: reducing the difference between these radii results in softer valve closing characteristics.
The diaphragm is normally produced via liquid silicone injection moulding: in such cases, moulding can be profitably realised with a central injection point (i.e. in correspondence with the centre of the diaphragm disc), which avoids any kind of interruption or discontinuity on either of the disc""s sealing lips. This ensures perfect hermetic sealing during operation when the valve is in the closed position.
According to another aspect of the invention, the said annular peripheral section can have a thickness equal to that of the said central disc. The said annular peripheral section can be inserted between the said first and second tubular elements without axial blocking and, in the valve closed position, the said diaphragm can have a planar shape.
This characteristic simplifies manufacture of the check valve, above all in relation to the production of the diaphragm and its assembly with the tubular elements, as well as improving operating reliability.